1. Field of the Invention
The present invention relates to the monitoring of a liquid, in particular a liquid contained in a tank of an SCR (Selective Catalytic Reduction) system in a motor vehicle, the liquid being an aqueous urea solution.
2. Description of the Related Art
Legislation on vehicle and heavy goods vehicle emissions stipulates, amongst other things, a reduction in the release of nitrogen oxides NOx into the atmosphere. One known way to achieve this objective is to use the SCR process which enables the reduction of nitrogen oxides by injection of a reducing agent, generally ammonia, into the exhaust line. This ammonia may derive from the thermolytic decomposition of an ammonia precursor solution, whose concentration may be the eutectic concentration. Such an ammonia precursor is generally a urea solution (eutectic at 32.5% by weight of urea).
With the SCR process, the high discharge of NOx produced in the engine during combustion at optimized efficiency are treated in a catalyst as they exit the engine. This treatment requires the use of the reducing agent at a precise concentration and of extreme quality. The solution is thus accurately metered and injected into the exhaust gas stream where it is hydrolysed before converting the nitrogen oxide (NOx) to nitrogen (N2) and water (H2O).
To do this, it is necessary to equip the vehicles with a tank containing an additive solution (generally aqueous urea solution).
However, it is important to be able to monitor the quality of the reducing agent in the tank to be able to dose it in an accurate manner.